The present invention relates to a surface acoustic wave apparatus, and more particularly, to an acoustic-coupling surface acoustic wave apparatus which includes a resonator composed of a plurality of acoustically coupled interdigital transducers.
Surface acoustic wave apparatuses which utilize a surface acoustic wave (SAW) generated by the piezo-electric effect have been recently used in wide applications, including a transceiver filter, an antenna duplexer and the like for portable telephones because of their advantages of small size, light weight, and high reliability.
The SAW apparatus comprises a plurality of interdigital transducers (hereinafter called “IDT”) for exciting surface acoustic waves, and reflectors for confining the surface acoustic waves excited by the associated IDT's. The IDT's and reflectors are formed on a piezo-electric substrate, where the IDT's are electrically or acoustically connected to the associated reflectors.
Known IDT connecting structures include a ladder-based structure for connecting a plurality of IDT's in a ladder shape, and an acoustic coupling type structure for acoustically coupling a plurality of IDT's which are disposed within a propagation path of a surface acoustic wave. While the number of connections for the IDT's is selected as appropriate in accordance with particular characteristics intended by the SAW apparatus, the acoustic-coupling type structure is generally advantageous over the ladder-based structure in a reduction in size resulting from a smaller number of reflectors contained therein and a shorter electrode length (shorter wiring pattern length) for connecting the resonators to each other, and the ability to omit losses within the reflectors and due to the connection electrode resistance (wiring resistance) to keep an insertion loss small.
Such SAW apparatuses have also been disclosed by JP-A-8-242140 (Patent Document 1), JP-A-9-505974 (Patent Document 2), and JP-A-2004-112238 (Patent Document 3).